Jake and Nog discuss this in In the Cards:
NOG It's my money, Jake. If you want to bid at this
auction, use your own money.
JAKE I'm Human, I don't have any money.
NOG It's not my fault that your species decided to
abandon currency-based economics in favor
of some philosophy of self-enhancement.
JAKE (defensive) Hey, watch it. There's nothing wrong with our philosophy.
(with pride) We work to better ourselves and the rest of Humanity.
NOG (confused) What does that mean exactly?
JAKE It means... (reaching) ... it means we don't need money.
NOG Well if you don't need money, then you certainly don't need mine.